Infinite dilution activity coefficient measurements for limonene as a green solvent for separation

Abstract

There is an increasing call from the international communities for the replacement of traditional petrochemical solvents used by the chemical and allied industries in the separation processes. This has led to the new interest in finding alternative “green” solvents, which can be used to optimize the separation processes of non-ideal or close boiling mixtures for better separation. This study focuses on investigating limonene as a “green” solvent to be utilized as a separating agent for separation processes. Limonene is a non-polar monoterpene solvent extracted from essential oils of the citrus peels. The extraction and distillation of this biomass extracted solvent releases fewer toxic pollutants and volatile gases, and as a result it has minimal impact to the environment. The infinite dilution activity coefficients (IDACs) for various solutes, which include alkanes, alkenes, alkynes, cycloalkanes, heterocycles, alcohol, aromatics, ketones, ethers, nitrile and water in the limonene solvent were measured using gas-liquid chromatography at (303.15, 313.15, 323.15 and 333.15) K. Through the experimental infinite dilution activity coefficients (IDACs), the values of partial molar excess enthalpy at infinite were obtained using the Gibbs-Helmholtz equation. To evaluate its potential of limonene as a mass transfer separation agent, its selectivity and capacity were calculated from the experimental limiting activity coefficients and were compared with ionic liquids and conventional solvents. From the results of this study, it was generally observed that for all solutes the activity coefficient at infinite dilution decreased with the increase of temperature and increased with the increase of alkyl chain length of the solute. The triple bond alkyl solutes had a strong interaction with the limonene, due to their low values of activity coefficients at infinite dilution. In some selective test cases, the selectivity and capacity for the separation of hexane/hex-1-ene and ethanol/water showing promising results when compared with ILs. The selectivity and capacity for the separation mixture of heptane/benzene, octane/ethylactetate, heptane/pyridine, octane/pyridine, and octane/thiophene indicated that the limonene was not suitable as the extraction solvent when compared with other ILs and conventional solvents. However, more investigation of limonene must be conducted through measurements liquid-liquid equilibrium and vapour-liquid equilibrium. Such data would provide useful information and understanding into the separation of hexane/hex-1-ene and ethanol/water mixtures. Green solvents extracted from biomass which have high boiling temperatures also be studied and compared with limonene solvent.